A Phase Error Elimination Method in Asynchronous Communication System

Previous ranging or localization systems achieve an accurate time of flight (TOF) estimation based on strict time synchronization between transmitter and receiver, which is difficult to realize in a practical communication system. To tackle this problem, we propose a phase error elimination method to achieve accurate ranging in an asynchronous manner. We implement the proposed method using a software radio platform, and the real experimental results show that the proposed method can achieve a ranging accuracy of 5.6 cm,

I. Introduction

With the increasing demand for location awareness services, indoor localization technology has obtained extensive attention. In recent years, RF-based indoor localization has been significantly advanced [1]. In general, we can extract the received signal strength indicator (RSSI) or channel state information (CSI) for indoor localization. Since the information provided by RSSI is relatively rough, the performance is usually limited [2]. Compared with RSSI, more delicate channel information can be extracted from CSI for more accurate localization. However, the CSI directly obtained from the device is distorted with various errors due to the imperfection and lack of synchronization of the transmitter and receiver hardware. This paper mainly studies the following two phase errors. The first is caused by phase-locked loop (PLL). Concretely, each time the transmitter and receiver start working, random initial phases are generated, which is known as PLL phase offset (PPO). The second is caused by carrier frequency offset (CFO) between transmitter and receiver [3]. This paper aims to restore the distorted CSI by eliminating the PPO and CFO for accurate ranging when the transmitter and receiver work in an asynchronous manner.